The present invention relates to “medical devices” as defined by the Jun. 14, 1993 Directive 93/42/EEC of the Council of the European Communities, more specifically to the “active implantable medical devices” as defined by the Jun. 20, 1990 Directive 90/385/EEC of the Council of the European Communities. This definition in particular includes devices that continuously monitor the cardiac rhythm and deliver if and as necessary to the eart electrical pulses for cardiac stimulation, resynchronization, cardioversion and/or defibrillation, in case of a rhythm disorder detected by the device. It also includes neurological devices and cochlear implants, as well as devices for pH measurement and for intracorporeal impedance measurement (such for measuring a transpulmonary impedance or an intracardiac impedance).
The present invention relates more particularly to those devices that involve autonomous implanted devices without any physical connection to a main (master) device that may be implanted (such as a generator for delivering stimulation pulses) or not implanted (such as an external programmer or device for remote monitoring of a patient). The autonomous implanted device communicates with the main or master device using a wireless communication technology.
Autonomous active implantable medical devices of the type involved in the present invention are also known as “leadless capsules” or more simply “capsules” to distinguish them from the electrodes or sensors placed at the distal end of a lead, which lead is connected at its opposite, proximal end, to a generator and is traversed throughout its length by one or more conductors connecting by galvanic conduction the electrode or the sensor to that generator. Such leadless capsules are, for example, described in U.S. Pat. Publication No. 2007/0088397 A1 and WO 2007/047681 A2 (Nanostim, Inc.) or in U.S. Pat. Publication No. 2006/0136004 A1 (EBR Systems, Inc.). These leadless capsules can be implanted epicardially, i.e., fixed to the outer wall of the heart, or endocardially, i.e., fixed to the inside wall of a ventricular or atrial cavity.
The attachment to the heart wall is usually obtained by a protruding anchoring helical screw, axially extending from the body of the capsule and designed to penetrate the heart tissue by screwing to the implantation site.
The leadless capsule typically includes detection/stimulation circuitry to detect (collect) depolarization potentials of the myocardium and/or to apply stimulation pulses to the implantation site (also called the stimulation site) where the capsule is located. The capsule then includes an appropriate electrode, which can be an active part of the anchoring screw, for electrically coupling to the mycocardium. It can also incorporate one or more sensors for locally measuring the value of a patient parameter, such as the oxygen level in the blood, the endocardial cardiac pressure, the acceleration of the heart wall, and the acceleration of the patient as an indicator of activity. Of course, for the remote exchange of data, the leadless capsules incorporate a transmitter/receiver for wireless communications with another device.
It should be understood however, that the present invention is not limited to one particular type of autonomous leadless capsule or implanted device; and is equally applicable to any type of leadless capsule, regardless of its functional purpose.
The energy source is one of the major weaknesses of leadless capsules because, being autonomous, it is not possible to provide energy through a lead conductor as with conventional or wired leads. Although energy harvesting devices and techniques have been proposed, to date only leadless capsules having battery power supply systems are truly operational. But given the very restrictive volume constraints, the autonomy of these batteries is limited, so that the currently available leadless capsules have a limited life span of around six months to two years, and must be regularly replaced.
The replacement of a leadless capsule, in addition to the frequent reiteration of a particularly invasive surgery, causes several problems:                First, the former site of implantation, which was perhaps optimal (especially if it was determined according to a mapping optimization procedure) is not easily traceable;        Second, further trauma to the tissues are caused by the explantation of the old device and the implantation of a new one; and        Third, when the device at its end of life cannot be removed and must be left in place, it remains as a foreign and invasive parasitic element, which can become problematic over the years particularly with successive device implantations.        
The above problems also arise elsewhere, regardless of the cause of the leadless capsule replacement, such as for a defective electronic circuit, replacement by a newer version device, and an element generating an infection.
Moreover, the introduction to the implantation site of a leadless capsule of a relatively large size requires tools of appropriate size, the use of which may be traumatic for the patient.
Finally, in all the systems proposed so far, the axis of fixation of the leadless capsule (typically, the axis of the anchoring screw) is the same as the axis of introduction of the device. For an endocardial device, this means that the anchoring system is at the end of the elongated cylindrical body constituting the body of the leadless capsule, which must necessarily be fixed perpendicularly to the heart wall. This configuration increases the invasiveness of the implanted system in relation to the heart function, particularly because of greater interference with blood flow and movement of the heart walls.